U.S. Pat. No. 5,671,054 discloses a method and an apparatus for determining the position of patterns on substrates that have a specific thickness. The substrate is placed onto a measurement stage that, in order to support the substrate, has three defined point-like support elements. The thickness of the substrate is determined using a reference substrate that is first measured. Then the substrate provided for measurement is measured. A data processing element then calculates the corresponding thickness differences from the differences between the reference substrate and the substrate to be measured, and incorporates them into the calculation for further determination of the position of the pattern. This arrangement has a considerable disadvantage, however, in that it is not very flexible, since only fixed mask sizes can be used or measured in this case. It is moreover problematic that if masks with different mask thicknesses need to be measured, the focal plane changes and is no longer located exactly on the surface of the substrate.
A substrate holder is also known from the article “Advanced Mask Metrology System for Up to 4 Gbit DRAM,” published in SPIE, Vol. 3096-0277-786X/97, pages 433–444. This presents a universal substrate holder that has the support points or support elements arranged correspondingly on the substrate holder surface in accordance with the various sizes of the substrate types used. The support elements are configured such that they differ in height. For example, the support elements for the substrates with smaller dimensions are not as high as the support elements for substrates with larger dimensions. A disadvantage of this substrate holder is that it is not suitable for transmitted light.